A communications method as a successor of W-CDMA and HSDPA, namely, Long Term Evolution (LTE) has been considered by a W-CDMA standardization organization 3GPP. As a radio access method, Orthogonal Frequency Division Multiplexing (OFDM) is under consideration for downlink, and Single-Carrier Frequency Division Multiple Access (SC-FDMA) is under consideration for uplink (see Non-patent Publication 1, for example).
In OFDM, a frequency band is divided into plural narrow frequency bands (sub-carriers), and data are placed on the respective divided frequency bands to carry out transmission. The sub-carriers are densely arranged in a frequency direction, allowing the sub-carriers to be partly overlapped without causing interference, thereby realizing high speed transmission and improving frequency usage efficiency.
In SC-FDMA, a frequency band is divided into plural narrow bands, and different narrow bands are used by different terminal devices, so that interference between the user terminals can be reduced. According to SC-FDMA, which is characterized in that variations in the transmission electric power are reduced, a large coverage area and low energy consumption can be realized.
Generally, fluctuations in a propagation environment such as fading take place in mobile communications. Due to fading, transmission quality, namely, a bit error rate characteristic is greatly degraded. In a third generation mobile communications system such as International Mobile Telecommunication-200 (IMT-2000), transmission power control that changes transmission power depending the fluctuations in the propagation environment is applied as a technique for reducing degradation of the transmission quality due to fading.
On the other hand, in LTE, an Adaptive Modulation and Coding (AMC) that changes a frequency bandwidth, a modulation scheme, a coding rate, and a data size depending on the fluctuations in the propagation environment is applied as a technique for reducing degradation of the transmission quality due to fading. Therefore, the transmission power per unit frequency band for a data signal in LTE, namely, the transmission power per sub-carrier is constant. In the following, the data signal to which the AMC is applied is referred to as a “normal data signal”.
However, application of the transmission power control is under consideration even in LTE for a data signal such as Voice over Internet Protocol (VoIP) and the like, which is transmitted at about a constant transmission rate (see Non-patent Publication 2, for example). In LTE, a transmission method for transmitting the data signal such as VoIP and the like, which is transmitted at about a constant transmission rate, is called persistent scheduling or semi-persistent scheduling.
In addition, it is being considered that a ratio of a transmission power per sub-carrier of a Downlink Reference Signal, which is a pilot signal, and a transmission power per one sub-carrier of a normal signal be set to a fixed value, and a mobile station use the fixed value to carry out demodulation of an orthogonal amplitude modulation, such as a 16 Quadrature Amplitude Modulation (QAM) or 64 QAM modulation (see Non-patent Publication 3, for example).
In the demodulation of 16 QAM or 64 QAM, because amplitude estimation has to be carried out, the transmission characteristic can be improved by carrying out demodulation using the above fixed value. In this case, because the transmission power per sub-carrier of the Downlink Reference Signal is always constant, the transmission power per sub-carrier of the normal data signal is also always constant.
When there are a time period when the Downlink Reference Signal is transmitted and a time period when the Downlink Reference Signal is not transmitted, as a method to make the transmission power per sub-carrier of the normal data signal even in both time periods, it is considered that mapping of the normal data signal to a predetermined sub-carrier be prohibited in the time period when the Downlink Reference Signal is transmitted (see Non-Patent Document 3). Information on which sub-carrier is subject to the prohibition of the normal data signal mapping has to be system-specific. It is considered that the sub-carrier for which mapping of the normal data signal is prohibited be associated with the ratio (a fixed value) of the transmission power per sub-carrier of the Downlink Reference Signal and the transmission power per sub-carrier of the normal data signal.
In the method where the mapping of the normal data signal to the predetermined sub-carrier is prohibited, it is presupposed that a base station apparatus transmits at the maximum transmission power (rated power). When the base station apparatus cannot transmit at the maximum transmission power (rated power), the transmission efficiency is reduced because all the transmission power resources are not used up.    Non-patent Publication 1: 3GPP TR 25.814 (V7.0.0), “Physical Layer Aspects for Evolved UTRA,” June 2006    Non-patent Publication 2: R1-070098, “Persistent Scheduling in E-UTRA,”, January 2007    Non-patent Publication 3: R1-070088, “Power Boosting of Reference Signal in E-UTRA Downlink,”, January 2007